The present invention relates generally to printed circuit system boards and, more specifically, to a LVD SCSI bus.
A printed circuit system board (PCSB) is a printed circuit board used in a computer which contains the computer central processing unit (CPU) and is thus the primary circuit board of the computer. A printed circuit board is a device used for interconnecting separate circuitry, electrical components and devices used by a computer. A common standard used for computer input/output (I/O) communications is Low Voltage Differential (LVD) Small Computer Systems Interface (SCSI). (There are various types of SCSI buses other than LVD SCSI buses but it is to be understood that any reference to xe2x80x9cSCSIxe2x80x9d in this patent application, unless otherwise indicated, is a reference to LVD SCSI.) A typical LVD SCSI bus found on a PCSB includes a LVD SCSI controller device such as an ASIC which is mounted on one surface layer of the PCSB. The SCSI controller controls the LVD SCSI signals sent between the computer""s CPU and SCSI devices, such as hard drives, DVD drives, etc., which are connected to the SCSI bus. In currently used PCSB""s the LVD SCSI bus includes a number of signal traces or conductors which extend between the SCSI controller and a cable connector device mounted on the PCSB. The cable connector device is adapted to matingly receive a coupling member provided on one end of a computer cable. The other end of the computer cable is provided with another coupling member that is adapted to be attached to a cable connector mounted on a smaller, auxiliary, printed circuit board usually called a xe2x80x9cback plane.xe2x80x9d The auxiliary circuit board includes a series of signal traces which extend from the cable connector to one or more SCSI device connectors mounted on the back plane. The LVD SCSI device connector on the back plane may be a direct connector such as SCA-2 connector to which a LVD SCSI device may be directly mounted. The back plane further includes LVD SCSI terminator devices to which end portions of the SCSI traces are connected after connection thereof to the last direct connector. The terminators are active circuit devices which prevent signal reflection, etc.
Applicants have discovered that in LVD SCSI buses that certain signals which are not actively driven low, namely the RESET, SELECT and BUSY signals, are particularly subject to electrical interference problems which may degrade the performance of the LVD SCSI bus.
Applicants have discovered that by carefully controlling the arrangement spacing and layering of certain signal traces in an LVD SCSI bus that noise problems affecting bus performance may be significantly reduced. Techniques which may be employed individually or collectively include running RESET, SELECT and BUSY signal trace pairs in adjacent relationship; providing increased separation of RESET, SELECT and BUSY signal trace pairs from the other bus signal traces; running at least a portion of RESET, SELECT and/or BUSY signal trace pairs on a side of the associated PCSB opposite from the side where other bus signal traces are run.
Thus the invention may comprise a PCSB assembly including a PCSB; a first plurality of LVD SCSI bus signal trace pairs formed in the PCSB; a second plurality of LVD SCSI bus signal trace pairs formed in the PCSB and positioned next adjacent one another for the entire length thereof comprising a RESET signal trace pair, a SELECT signal trace pair and a BUSY signal trace pair.
The invention may also comprise a PCSB including a first surface layer comprising a plurality of LVD SCSI bus signal trace pairs and a second surface layer opposite the first surface layer comprising at least a portion of at least one signal trace pair selected from the group of: a LVD SCSI bus RESET signal trace pair; a LVD SCSI bus SELECT signal trace pair and a LVD SCSI bus BUSY signal trace pair; and excluding all LVD SCSI bus signal trace pairs other than those in the group.
The invention may also comprise a method of forming a PCSB comprising: forming a plurality of LVD SCSI bus signal trace pairs in a first exterior layer of the PCSB and forming at least a portion of at least one of a RESET, SELECT and BUSY signal trace pair of the LVD SCSI bus in a second exterior surface layer of the PCSB.
The invention may also comprise a method of forming a PCSB comprising: forming a plurality of LVD SCSI bus signal trace pairs in at least one exterior layer of the PCSB including forming RESET, SELECT and BUSY signal trace pairs; maintaining the RESET, SELECT, and BUSY signal trace pairs in next adjacent relationship for their entire length whereby no other LVD SCSI bus signal trace pairs are interposed between adjacent ones of the RESET, SELECT, and BUSY signal trace pairs.